The .po file has a header which contains information about the project, of you as a new translator and some character set information. Except for you complementing your name into the "Last-Translator" field, you don't need to do anything about it.
Translation structure
The .po file will contain a structure like
Your task will be to put your translation in the quotes of msgstr
including all spaces and special characters:
c-format
There are also c-Strings which look like
which you'd have to translate including %s
(which is a place holder) and \n
(which is a control character).
Big messages
Sometimes there are big messages like
Just do it the same: